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Fatty acids. Part 50. 13C nuclear magnetic resonance studies of olefinic fatty acids and esters
Chemistry and Physics of Lipids 18 (1977) 115-129 © Elsevier/North-Holland Scientific Publishers Ltd.
FATTY ACIDS. PART 50 *. 13C NUCLEAR MAGNETIC RESONANCE STUDIES OF OLEFINIC FATTY ACIDS AND ESTERS F.D. GUNSTONE, M.R. POLLARD, C.M. SCRIMGEOUR and H.S. VEDANAYAGAM Department of Chemistry, University of St. Andrews, Fife KY16 9ST, Scotland Received May 4th, 1976,
accepted August 4th, 1976
The 13C-NMR spectra of 48 cis alkenoic acids and esters (C8-C20), 18 trans alkenoic acids and esters ( C 9 - C 1 8 ) , and 26 polyenoic acids and esters (C18-C22) are reported and interpreted. The characteristic features of such spectra which permit structural assignments to be made are discussed.
I. Introduction Our study of the IH-NMR spectra of alkenoic and alkynoic acids and their derivatives [ 1] is being followed by a similar study of their 13C-NMR spectra and we have 'already reported on a range of saturated acids and esters and on 47 acetylenic acids [2]. In this paper we describe a similar study of olefinic acids and esters containing 1 - 4 cis double bonds, acids and esters with one trans double bond, and acids and esters with mixed unsaturation. Information on compounds of this type has already been reported by Stoffel et al. [3], Batchelor et al. [4], Cronan and Batchelor [5], Batchelor et al. [6], Bus and Frost [7], Barton [8] and Tulloch and Mazurek [14] who have drawn attention to the very distinctive signals associated with the olefinic, allylic, A1--3, and w l - 3 carbon atoms. Building on these results and making use of our data on the shorter chain acids (C8-C14) we have made a careful study of deshielding influences.
I1. Results and discussion Our results are set out in table 1. The allocation of chemical shifts is based on information available in the published work already listed and on the assumption that the influence of a functional group on the chemical shift of neighbouring carbon atoms is consistent through a range of structures. Chemical shifts are given to two
* Fatty Acids. Part 49. J. Sci. Food Agric. 27 (1976) 675. 115
116
F.D. Gunstone et al., 13C-NMR studies of olefinic acids
decimal places as obtained from the spectrometer and are considered to be reproducible to -+0.05 p p m . For a few o f the molecules the n u m b e r of signals is the same as the n u m b e r of carbon atoms and the allocation of resonances to individual carbon atoms is then not difficult. When the n u m b e r of signals is less than the n u m b e r of carbon atoms assignment is m o r e difficult (and in a few cases may even be in doubt). Also the chemical shifts for i n c o m p l e t e l y resolved signals are likely to be less accurate than w h e n a shift applies to a single carbon atom. Peak heights for one-carbon signals are n o t always identical and it is difficult to assign the correct n u m b e r of carbon atoms to overlapping resonances from peak heights alone. A. Olefinic carbon atoms in m o n o e n o i c acids and esters O f the 66 cis and trans m o n o e n o i c acids and esters listed in table l all except 6 show two resonances for their olefinic carbon atoms. These are the 17 : 1 12c (129.89) and 20 : 1 1 l e (129.88) m e t h y l esters, the 18 : 1 12c (129.94) and 18 : 1 13c (129.90) acids, and the 18 : 1 12t (130.41) and 18 : 1 13t (130.39) acids. The mean values o f Table 1 Allocation of resonance signals (ppm downfield from Me4Si) for olefinic acids and esters. Table 1A. C 8-C14 cis alkenoic acids. C(1) 8: 1(7) 10: 1(8) 11 : 1(4) (5) (6) (8) (10) 12: 1(3) (5) (7) (10) 13 : 1(3) (5) (6) (7) (9) (10) 14 : 1 (3) (4) (5) (6) (7) (8)
180.64 180.54 180.01 180.50 180.42 180.59 180.34 178.51 180.44 180.46 180.53 178.48 180.15 180.41 180.58 180.53 180.66 178.68 180.00 180.46 180.30 180.39 180.63
C(2) 34.16 34.18 34.35 33.58 34.09 34.21 34.19 32.78 33.56 34.20 34.18 32.8l 33.55 34.09 34.18 34.18 34.22 32.73 34.35 33.55 34.08 34.22 34.20
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
24.59 24.71 22.66 24.74 24.39 24.75 24~76 120.01 24.71 24.69 24.73 120.09 24.72 24.37 24.67 24.73 24.76 120.04 22.65 24.70 24.37 24.70 24.75
28.59 29.00 127.04 26.55 29.02 29.04 29.16 134.21 26.53 28.79 29.14 134.17 26.52 29.17 28.79 29.12 29.30 134.14 127.04 26.53 29.28 28.80 29.04
28.59 28.92 131.94 128.23 26.86 28.94 29.28 27.48 128.20 29.42 29.14 27.49 128.19 26.85 29.44 29.12 29.30 27.47 131.93 128.19 26.85 29.42 28.99
33.61 29.36 27.30 131.44 129.04 29.60 29.28 29.31 131.42 27.03 29.14 29.36 131.44 129.03 27.05 29.12 29.30 29.33 27.30 131.43 129.01 27.05 29.59
138.71 26.77 29.69 27.29 130.57 27.07 29.16 29.31 27.32 129.48 29.14 29.36 27.3l 130.63 129.46 29.73 29.30 29.33 29.70 27.32 130.64 129.44 27.22
114.53 130.67 29.05 29.46 27.01 129.11 29.00 29.31 29.73 130.29 29.14 29.58 29.75 27.32 130.33 27.24 29.83 29.65 29.44 29.75 27.32 130.29 129.64
F.D. Gunstone et al., 13C-NMR studies of olefinie acids
117
129.90 (cis) and 130.40 (trans) compare with values of 29.84 and 29.80 for undisturbed CH 2 groups in long-chain esters and acids respectively [2]. The two signals corresponding to the olefinic carbon atoms of the remaining monoenes have been allocated on the basis of values previously recorded [3,4,6-8] and particularly on the results of Cronan and Batchelor [5] who confirmed the allocation for 16 : 1 9c by the study of esters produced biosynthetically from 13C-labelled acetate. Our results show that olefinic carbon atoms are influenced by a COOH or COOMe group up to A10 or A11 or by the end methyl group up to w4 and, in appropriate shortchain compounds, by both influences in an additive manner. The chemical shifts for cis and trans olefinic carbon atoms in long-chain acids/esters are listed in table 2. The 11 : 1 8c and 13 : 1 9c acids are representative of compounds in which olefinic carbon atoms are influenced by both COOH and CH3 groups: the observed shifts are very close to those calculated from the information given in table 2. 11 : 1 8 c ( w 3 ) 13 : 19c(6o4)
C(8) C(9) C(9) C(10)
129.90-0.25-0.53= 129.12 129.90 + 0.25 + 1.63 = 131.78 129.90-0.11 +0.23=130.02 129.90 + 0.15 - 0.25 = 129.80
C(I1)
C(12)
C(13)
C(14)
14.13 14.08 13.99 12.72 22.74 22.71 22.70 22.64 22.95 20.60 31.97 32.03 31.98 31.93 31.85 31.65
14.11 14.08 14.08 14.08 13.79 14.40 22.73 22.73 22.74 22.72 22.71 22.67
14.10 14.12 14.10 14.10 14.08 14.07
C(9)
C(IO)
123.83 31.87 31.6l 32.01 131.78 33.86 29.31 29.05 27.03 26.89 29.63 29.29 29.76 27.27 130.00 27.16 29.65 29.70 29.40 29.79 27.30 130.14
12.71 22.66 14.10 22.64 14.06 2 2 . 4 1 13.98 20.60 14.38 139.04 114.24 3 1 . 8 9 22.73 3 1 . 8 4 22.71 3 2 . 0 4 22.40 130.83 1 2 3 . 6 5 29.36 31.98 29.29 31.93 29.08 31.85 29.44 31.62 1 2 9 . 7 9 29.73 129.29 1 3 1 . 6 2 29.65 29.33 29.70 29.44 29.58 29.40 29.28 29.28 29.79 29.05 27.22 29.59
obs. obs. obs. obs.
129.11 131.78 130.00 129.79
118
F.D. Gunstone et al., 13C-NMR studies of olefinic acids
Table lB. C16 C20 cis alkenoic acids and esters.
16: 1(8)* 17 : 1(12)* 18:1(2) (2)* (3) (3) * (4) (4)* (5) (5)* (6) (6)* (7) (7)* (8) (9) (9)* (10) (11) (12) (13) (14) (15) (17) 2 0 : 1 (11)*
C(1)
C(2)
174.26 a 174.06 b . . . 166.53 c 178.52 172.08 d 180.04 173.10 e 180.45 173.81 f 180.51 173.57 g 180.30 173.87 h 180.54 180.55 J 180.46 180.55 i80.53 180.54 180.58 180.61 180.63 173.93 k
34.14 34.14 . 119.41 33.12 32.80 34.27 34.21 33.58 33.48 34.13 33.98 34.22 34.08 34.22 34.24 34.12 34.22 34.22 34.31 34.18 34.25 34.23 34.21 34.t2
C(3) 25.01 25.06 150.69 120.55 121.00 22.66 22.98 24.74 25.05 24.39 24.76 24.73 25.00 24.78 24.80 25.08 24.81 24.76 24.82 24.74 24.78 24.79 24.78 25.08
C(4)
C(5)
C(6)
C(7)
C(8)
29.14 28.97 29.62 27.21 29.39 29.39 29.63 29.63 24.78 + 29.34 29.17 29.74 29.61 * 29.13 * 29.26 4 29.90 133.76 27.49 29.46 29.46 133.40 27.54 29.55 29.90 127.09 131.99 27.33 29.79 127.53 131.54 27.35 29.91 26.58 128.21 131.44 27.36 26.69 128.44 131.21 27.37 29.23 26.88 129.01 130.62 29.51 27.02 129.18 130.48 28.88 29.51 27.13 129.45 28.95 29.51 27.14 129.49 29.08 28.96 29.48 27.28 29.22 29.22 29.22 29.83 29.28 29.28 29.28 29.83 29.22 29.35 29.35 29.35 29.17 29.32 29.49 29.49 29.40 29.40 29.56 29.56 29.16 29.34 29.64 29.81 29.17 29.40 29.69 29.69 29.21 29.39 29.57 29.75 29.19 29.32 29.75 29.75 29.38 29.45 29.45 29.58
129.68 29.63 29.74 29.90 29.78 29.90 29.48 29.57 29.81 29.83 27.36 27.43 130.31 130.22 129.65 27.31 27.32 29.85 29.32 29.56 29.64 29.69 29.75 29.75 29.38
Esters. * Assignments uncertain (see text). Also signals at: 51.38 (a), 51.27 (b), 50.71 (c), 51.56 (d), 51.21 (e), 51.25 (f), 51.56 (g), 51.22 (h), 51.21 (j), 51.22 (k), 22.80 and 14.12 (1).
Our results suggest t h a t for m o n o e n e acids o f esters o f k n o w n c h a i n - l e n g t h ( a n d s o m e t i m e s w h e n t h e c h a i n - l e n g t h is n o t k n o w n ) the c h e m i c a l shift o f t h e olefinic c a r b o n a t o m s is sufficient to s h o w w h e t h e r the d o u b l e b o n d has cis or trans configur a t i o n and to i n d i c a t e its p o s i t i o n e x c e p t in those few c o m p o u n d s w h e r e only o n e olefinic signal is o b s e r v e d [7,8].
B. Olefinic carbon atoms in polyunsaturated acids and esters T h e diene acid/ester s p e c t r a c o n t a i n 4 signals c o r r e s p o n d i n g to u n s a t u r a t e d carb o n a t o m s . We assume t h a t each olefinic c e n t r e m a y be i n f l u e n c e d b y the acid (ester) group, t h e e n d m e t h y l , a n d the s e c o n d d o u b l e b o n d in an additive m a n n e r , and we
P2D. Gunstone et al., 13C-NMR studies o f olefinie acids
119
c(9)
C(10)
C(ll)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
130.13 29.39 29.74 29.90 29.78 29.90 29.79 29.91 29.48 29.51 29.76 29.93 27.39 27.36 130.17 129.78 129.78 27.30 29.82 29.40 29.64 29.69 29.75 29.75 29.90
27.21 29:87 29.74 29.90 29.78 29.90 29.79 29.91 29.81 29.83 29.45 29.59 29.81 29.82 27.28 130.09 130.02 129.83 27.29 29.56 29.34 29.69 29.75 29.75 27.34
29.84 27.30 29.74 29.90 29.78 29.90 29.79 29.91 29.81 29.83 29.76 29.93 29.51 29.51 29.70 27.31 27.32 130.00 129.89 27.29 29.81 29.40 29.57 29.75 129.88
29.31 129.89 29.74 29.90 29.78 29.90 29.79 29.91 29.81 29.83 29.76 29.93 29.81 29.82 29.48 29.83 29.90 27.30 129.96 129.94 27.27 29.69 29.39 29.75 129.88
29.31 129.89 29.74 29.90 29.78 29.90 29.79 29.91 29.81 29.83 29.76 29.93 29.81 29.82 29.70 29.47 29.46 29.85 27.29 129.94 129.90 27.33 29.75 29.75 27.34
31.95 27.01 29.74 29.90 29.78 29.90 29.79 29.91 29.81 29.83 29.76 29.93 29.81 29.82 29.70 29.68 29.68 29.35 29.82 27.29 129.90 130.16 27.21 29.25 29.90
22.72 32.09 29.46 29.61 29.46 29.55 29.51 29.57 29.48 29.5l 29.45 29.59 29.51 29.51 29.48 29.47 29.46 29.35 29.08 29.40 26.99 129.66 129.39 29.09 29.38
14.10 22.42 32.03 32.15 32.04 32.15 32.06 32.17 32.06 32.10 32.04 32.18 32.10 32.08 32.06 32.06 32.07 32.01 31.87 31.64 32.06 29.69 131.54 33.91 29.58
14.0l 22.76 22.86 22.78 22.88 22.75 22.91 22.79 22.83 22.78 22.89 22.82 22.81 22.80 22.80 22.79 22.76 22.72 22.68 22.40 22.96 20.60 139.13 29.46
14.12 14.15 14.13 14.17 14.13 14.16 14.13 14.14 14.11 14.18 14.13 14.12 14.12 14.13 14.11 14.12 14.10 14.09 14.00 13.80 14.41 114.15 32.071
use t h e results in table 2 to find values for the i n f l u e n c e o f o n e d o u b l e b o n d o n ano t h e r b y selecting those t h a t give the best fit. These i n f l u e n c e s are c o n v e n i e n t l y repr e s e n t e d b y greek letters, thus:
-CH ~3'
= CHCH2CH = CH/3
a
- CH = C H C H z C H z C H 2 C H = C H - . 6'
6
3'
/3
a
Consider, as an e x a m p l e , the 8c 12c a n d 6c 10c C18 diene acids. T h e c h e m i c a l shift o f each olefinic c a r b o n a t o m is given b y C(8) C(9) C(12) C(13)
129.90 129.90 129.90 129.90
+ + +
0.25 + 7 ' 0.25 + 3' 3' 3''
C(6) C(7) C(10) C(11)
129.90 129.90 129.90 129.90
+ +
0.88 0.72 0.07 0.10
+ + + +
3" 3' 3' 3''
120
F.D. Gunstone et al., 13C-NMR studies o f olefinic acids
Table 1C. C 9 C18 trans alkenoic acids and esters. C(1) 9 : 1(7) 10 : 1 (7)* (8)* 12 : 1(8)* 16:1 (7)* (8)* 18 : 1(5) (6) (7) (7)* (8) (9) (10) (11) (12) (13) (14) (15)
174.16 m 174.06 n 174.08 p 174.09 q 173.89 r 173.86 s 180.58 180.51 180.53 173.65 t 180.43 180.61 180.62 180.57 180.57 180.59 180.59 180.57
C(2) 34.12 34.12 34.13 34.13 34.10 34.12 33.47 34.06 34.20 34.06 34.20 34.19 34.21 34.22 34.20 34.21 34.21 34.21
C(3) 24.94 24.95 25.04 25.05 24.97 25.09 24.57 24.22 24.63 24.99 24.74 24.75 24.76 24.77 24.77 24.77 24.78 24.78
C(4)
C(5)
C(6)
2 8 . 7 5 29.29 32.42 2 8 . 7 5 2 9 . 3 5 32.42 29.14 28.88 29.50 29.15 28.86 29.55 28.79 29.39 32.50 2 9 . 2 1 28.92 29.62 31.91 128.72 131.98 29.07 3 2 . 2 1 129.49 28.63 29.31 32.40 28.83 29.43 32.55 29.02 28.79 29.46 29.14 29.17 29.00 29.18 29.30 29.40 29.20 29.32 29.53 29.17 2 9 . 3 1 29.53 29.20 29.34 29.55 29.18 29.32 29.54 29.18 2 9 . 2 8 29.53
C(7)
C(8)
131.34 129.05 32.60 32.62 130.01 32.61 32.65 131.13 129.89 130.03 32.58 29.65 29.18 29.53 29.64 29.70 29.71 29.73
124.89 132.26 131.52 130.41 130.75 130.21 29.66 32.67 130.81 130.75 130.13 32.64 29.75 29.20 29.55 29.70 29.71 29.73
* Esters. Also signals at: 51.35 (m), 51.31 (n), 51.31 (p), 51.29 (q), 51.24 (r), 51.21 (s), 51.15 (t). These are fitted to the observed values in ways which give the most consistent values for 3"(+0.43, +0.51, +0.46, +0.51) and 3'( 0.71, - 0 . 7 1 , - 0 . 7 3 , - 0 . 7 5 ) . Average values obtained in this way from several dienes are listed in table 3. Similar values were reported previously [6] for/3 a n d / 3 ' ( - 1.83 and +0.30), y and 3"( 0.5 and +0.5), and c and e ' ( - 0 . 2 8 and +0.23). Of the dienes we examined only linoleic acid has been reported before. Our assignments agree with those of Batchelor et al. [6] but differ from those of Stoffel et al. [3]. In a similar examination of our 6 triene acids/esters values of/3 and/3' obtained from the dienes are used and values of e* and e*' are derived (see table 3). The symbol e* refers to the effect of the double bond on an olefinic carbon atom operating through another double bond and is not necessarily identical with the value e which does not operate through a double bond. The chemical shifts of the inner pair of olefinic carbon atoms depend only on/3 and/3' and the shifts observed in the trienes agree well (average +0.03 for 12 values) with those calculated on the basis of the and/3' values derived from the dienes. For the remaining 4 olefinic carbon atoms in each triene account must also be taken of values for e* and e*' and these are again selected to give the best fit between observed and calculated values. Although these are internally consistent the values from the two eo3 trienes differ slightly from those from the 4 6o6 trienes and the average values are quoted separately in table 3. It is not clear why these values should differ. The 6o3 values for e* and e*' hardly differ
F.D. Gunstone et al., 13C-NMR studies of olefi'nic acids
C(9)
C(10)
C(ll)
C(12)
C(13)
C(14)
17.87 25.68 124.75 130.41 32.74 130.64 29.30 29.75 32.67 32.79 130.67 130.23 32.68 29.73 29.21 29.63 29.71 29.73
14".01 17.87 34.83 29.81 32.76 29.66 29.30 29.76 29.87 32.68 130.54 130.31 32.69 29.72 29.27 29.54 29.73
22.85 13.65 29.39 29.67 29.39 32.09 29.87 29.35 29.35 32.09 29.78 29.78 29.78 29.78 29.67 29.75 29.75 29.75 2 9 . 3 1 29.65 29.76 29.76 29.43 29.87 29.87 29.87 29.72 29.28 29.72 29.72 32.66 29.76 29.28 29.60 130.47 32.68 29.75 29.26 130.35 130.43 32.69 29.73 32.65 130.41 1 3 0 . 4 1 32.65 29.76 32.69 130.39 130.39 29.26 2 9 . 7 1 32.69 130.63 29.53 29.28 29.73 32.65
C(15)
C(16)
22.83 22.84 29.47 29.45 29.45 29.58 29.46 29.4l 29.30 28.93 29.43 32.36 130.13 129.45
14.14 14.14 32.04 32.04 32.05 32.15 32.01 32.01 32.00 31.88 31.49 31.96 34.79 131.93
121
C(17)
22.78 22.76 22.78 22.87 22.76 22.76 22.77 22.73 22.62 22.27 22.82 25.65
C(18)
14,12 14.12 14.11 14.15 14.ll 14.11 14.11 14.10 14.07 13.96 13.64 14.04
from the e and e' values derived from the 18 : 2 (6, 12) and 20 : 3 (7, 13) dienes. For the two tetraenes examined (20 : 4 6o6 and 22 : 4 6o6) the/3 and/3' values from the dienes and the e* and e*' values from the 6o6 trienes are used. Again chemical shifts involving only these values give a good agreement between observed and calculated values (average of-+0.06 for 8 values). There is no difficulty in assigning the observed chemical shifts to the remaining olefinic centres in each compound but the 0"* and 0"*' values are less consistent than usual (see footnote to table 3). Table 3 also contains some values for systems other than all-cis polyenes. Cis and trans double bonds seem to exert a similar but not identical effect on each other whereas in the enynes examined the chemical shift induced in a triple bond by a nearby double bond differs markedly from the shift induced in the sp 2 carbon atoms by the triple bond. C. Allylic carbon atoms In a monoenoic acid or ester there is an easily recognised signal associated with the allylic carbon atoms. When not also influenced by CO2 H or CH3 end groups, this lies in the range 2 7 . 2 2 - 2 7 . 3 9 (mean 27.30) for a cis double bond and in the range 3 2 . 6 4 - 3 2 . 6 9 (mean 32.67) for a trans double bond. These values differ from each other and from the propargylic carbon atoms (18.85) reported in our earlier paper [2]. Different values are observed (tables 4A and 4B) when the allylic atom is also influenced by a COOH or CH 3 group or by a second double bond and these values are frequently of diagnostic value for recognising the position of unsaturated centres.
F.D. Gunstone et al., 13C-NMR studies of olefinic acids
122
Table ID. C18, C19 , C20 and C22 polyunsaturated acids and esters. C(1) All cis isomers 1 8 : 2 ( 5 , 12) (6,9) (6, 10) (6,11) (6, 12) (7, 12) (8, 12) (9, 12) 20 : 2(7, 13) (11,14)* All cis isomers 18:3(6,9,12)4 (6,9,12)* (9, 12, 15) 19: 3(7, 10, 13)* 20 : 3 (8, 11,14) (8,11,14)**
(11,14, 17)* 20:4(5,8,11,14)* 22:4(7,10,13,16) Other polyunsaturated 18 : 2(9t 12t)* (7t 12t)* (9c12t)* (9c 12t)* ~ (9t 12c) *s (9a12c)* (9c12a)* (9t 12a)* (9c12a 14c)*
C(2)
180.29 180.29 180.28 180.31 180.31 180.46 180.42 180.56 180.48 174.06 v
33.56 34.15 34.14 34.09 34.09 34.17 34.18 34.22 34.24 34.13
173.83 180.39 174.03 179.87 173.44 173.98 174.13 174.19 173.84 180.16
. 33.99 34.19 34.07 34.04 34.03 34.08 34.12 34.12 34.11 33.50 34.07
x y b' d' f' h' k' m
t
C(3)
C(4)
C(5)
C(6)
'C(7)
C(8)
26.56 29.14 29.21 29.20 29.22 28.80 29.08 29.21 28.82 29.38
128.29 26.90 26.91 26.95 26.89 29.41 29.00 29.21 29.44 29.47
131.29 129.29 129.48 129.34 129.13 26.95 29.56 29.21 27.18 29.55
27.29 128.74 129.89 130.28 130.41 129.73 27.32 29.72 129.54 29.55
29.' 25.' 27.1 26.! 27.~ 129.! 130.1 27.Z 130.~ 29.:
24.70 24.79 24.92 24.66 25.08 25.00 24.99 24.98 25.10 24.89 24.63
. 29.23 29.23 28.85 28.92 29.11 29.00 28.96 28.95 29.35 26.65 28.75
. 26.96 29.23 29.34 28.92 29.25 29.14 29.11 29.12 29.42 128.96 29.29
. 129.60 29.23 27.09 29.38 29.63 29.46 29.47 29.45 29.42 128.96 27.07
128.38 29.72 129.96 27.23 27.37 27.27 27.25 27.24 29.62 25.71 130.00
25.' 272 128.1 130. 130.( 130.1 130. 130. 29.: 128." 128.(
24.74 24.43 24.40 24.40 24.38 24.66 24.75 24.78 24.74 25.05
.
.
esters 174.15 q' 174.26 r' 174.08 s'
34.12 34.12 34.12
25.02 24.89 25.04
29.18 28.69 29.23
29.18 29.32 29.23
29.04 32.41 29.23
29.52 130.25 29.68
173.81 t'
34.07
25.08
29.28
29.28
29.28
29.70
32..' 130.~ 27.1 ~-27.: ~32.f
173.97 174.20 174.01 173.91
34.08 34.12 34.09 34.07
25.02 25.01 25.05 25.04
29.15 29.17 29.23 29.23
28.91 29.17 29.23 29.23
28.77 29.17 29.12 29.23
29.15 29.38 29.39 29.39
18A 27.] 32.: 27S
u' v' w' x'
* Esters. ** Methyl esters at 2 M, 1 M, 0.4 M, and 0.14 M concentration respectively. Hydrocarbon. Carbon atoms 1 - 9 have the same chemical shifts as carbon atoms 1 8 - 1 0 respectively. They are presented in this way to emphasize their similarity to acids/esters at the CH 3 end. Also signals at: 22.72 and 14.10 (u), 51.29 (v), 22.67 and 14.10 (w), 51.31 (x), 51.35 (y), 14.05 (z), 22.58 and 14.03 (a'), 51.08 (b'), 22.76 and 14.11 (c'), 51.29 (d'), 22.66 and 14.07 (e'), 51.36 (f'), 22.62 and 14.06 (g'), 51.39 (h'), 22.58 and 14.03 (j'), 51.19 (k'), 20.67 and 14.30 (1'), 51.40 (m'), 22.61 and 14.05 (n'), 29.29, 31.57, 22.60 and 14.05 (p'), 51.32 (q'), 51.39 (r'), 51.29 (s'), 51.19 (t'), 51.28 (u'), 51.36 (v'), 51.27 (w') and 51.26 (x').
F.D. Gunstone et al., 13C-NMR studies o f olefinic acids
C(9)
C(IO)
C(ll)
C(12)
C(13)
C(14)
C(15)
29.04 127.82 27.37 29.85 29.45 26,95 129,44 130,01 27,18 29.76
29.72 130.34 129.08 26.95 29,45 29.92 27.54 128,24 29.44 27.32
27.29 27.33 130.51 129.49 27.21 26.95 27.54 25.77 29.44 130.13
129.81 29.75 27.37 130.28 129.70 129.53 129.19 128.08 27.18 128.07
130.02 29.41 29.83 27.34 130.07 130.29 130.41 130.20 129.71 25.74
27.29 29.62 29.33 29.85 27.21 27.28 27.32 27.32 130.08 128.07
29.58 29.4l 29.33 29.11 29.45 29.41 29.56 29.48 27.18 130.13
31.64 32.00 31.97 31.92 31.63 31.60 31.64 31.67 29.82 27,32
22.68 22.75 22.74 22.75 22.67 22.64 22.69 22.69 29.06 29,49
128.14 130.17 25.71 127.94 128.07 127.96 127.93 127.91 29.82 128.25 25.71
128.37 128,46 127.94 128.19 25.68 25.80 25.73 25.71 25.70 27.37 25.71 128,41
25.77 25,74 25.76 128.39 128.26 128.28 128.28 128.27 128.27 130.28 127,97 128.01
127.81 127.74 128.33 25.71 128.38 128.36 128.36 128.36 128.39 127.87 128.65 25.71
130.41 130.42 128,33 127,71 25,68 25,80 25.73 25,71 25,70 25.75 25.71 128,01
27.34 27.33 25.68 130.40 127.71 127.88 127.75 127.73 127.71 128.33 127.63 128.59
29.46 29.44 127.28 27,27 130.43 130.27 130.36 130.41 130,44 128.33 130.51 25.71
31.66 31.64 131,88 29.34 27.20 27.37 27.27 27.25 27.24 25.71 27.29 127.64
22.66 22.66 20.68 31.58 29.38 29.56 29.46 29,47 29.45 127.31 29.39 130.50
14,06 14.07 14.31 22.62 31.55 31.74 31.63 31.59 31.59 131.86 31.59 27.27
130,92 32.08 130.31
128,79 29.62 127.94
35.68 32.08 30.55
128.65 130.08 128.40
131.08 130.72 130.84
32.59 32.62 32.64
29.18 29.32 29.23
31.50 31.47 31.53
22.60 22.59 22.64
14.06 14.07 14.08
130.27 130.64 79.79 131.14 131.59 131,54
127.96) 128.59 78.51 125.28 125.09 124.60
30,56
,f128.45 "127.83 125.28 78.40 77.62 92,37
22,69
14.10
22.66 22,29 22.35 22.27
14.07 14.00 14.02 13.76
-
17.24 17,24 22.07 18.02
130.79 32.67) 1 3 ( ) . 4 1 27.22 131.19 27.17 80.08 18.83 81.96 18.88 77.24 142.28
29.28 29.15 28.85 28.96 109.76
C(16)
123
~-31,59], "31.65 ~ 31.59 31.18 31.23 32.15
C(17)
C(18) 14.09 14.11 14.10 14,12 14.08 14.06 14.10 14.08 31.88 u 31.65 w
z a' c' e' ,gl J 1' n' P'
-9.85, -2.84, -1.70, -0.88, 0.44, 0.25, -0.11, -0.07, -0.01, +1.01, 0.53, +0.23,
+4.27(3) +2.05(2) +1.53(5) +0.72(4) +0.41(4) +0.25(2) +0.15(3) +0.10 +0.06 -6.33(2) +1.63(3) - 0 . 2 5 (2)
+20,79 + 3.50 + 1.64 + 1.31 + 0.58 + 0.32 + 0.23 + 0.12 0 -
-10.49, - 8.90, - 2.37, - 1.46, - 0.72, - 0.41, 0.22, 0.12, 0 -
-1.68, -0.91, -0.31, 0.27, -0.17, 0.09, -0.05, -0.95, +0.23,
. .
. .
+1.53 -0.27
+1.58 +0.73 +0.41 +0.27 +0.14 +0.07 +0.03
. .
Acids
Acids
Esters
Trans c o m p o u n d s *
Cix c o m p o u n d s *
. .
+1.39, -0.84, +0.20,
-0.38, -0.19, -
Esters
-5.92(2) +1.45 -0.23
-
+0.35 +0.24
* T h e shifts r e f e r to c a r b o n a t o m s n a n d n + 1 f o r t h e An series a n d to c a r b o n a t o m s m + 1 a n d m f o r t h e corn series. T h e n u m b e r o f e x a m p l e s is o n e e x c e p t w h e r e o t h e r w i s e i n d i c a t e d b y t h e value in p a r e n t h e s i s . t col values (acid) are 1 3 9 . 1 2 a n d 1 1 4 . 1 5 f o r t h e col a n d w 2 c a r b o n a t o m s .
2x 2 3 4 5 6 7 8 9 10 11 co 2 ? 3 4
Position of double bond
Table 2 C h e m i c a l shift i n d u c e d in o l e f i n i c c a r b o n a t o m s ( 1 2 9 . 9 0 p p m (cis) a n d 1 3 0 . 4 0 p p m (trans) w h e n u n d i s t u r b e d ) in m o n o e n o i c a c i d s a n d esters b y COOH (COOCH3) and CH 3 groups.
a,
125
F.D. Gunstone et al., 13C-NMR studies of olefinic acids Table 3 Chemical shift induced in unsaturated carbon a t o m s by a second unsaturated system.
cis-cis ~ t3 3, ,5 e g" e*(o.,3) e*(to6)
-1.86 -0.73 -0.37 -0.21 -0.12 -0.21 -0.34
+0.26(6) +0.48(4) +0.32(4) +0.14(4) +0.11(2) +0.10(4) +0.23(8)
trans-trans
eis-trans
-1.75
+0.67(2)
-2.03
-0.32
+0.28(2)
+0.45(4)
Less concordant values were derived for 0 ** ( - 0 . 0 5 , - 0 . 0 7 , +0.02, +0.12) and 0 **' (+0.03, +0.12, +0.05, 0.06). For explanation of symbols see text. Figures in parenthesis are the n u m b e r of values which have been averaged. The two n u m b e r s relate to the unprimed and primed values respectively. * Also values for 13and/3' for cis-enyne [ - 4 . 6 8 and +1.33 (en) and - 1 . 8 1 and - 0 . 1 8 (yne)] and trans-enyne systems [ - 5 . 4 5 and +1.36 (en) and - 2 . 5 7 and +1.77 (yne)].
D. The influence o f double bonds on neighbouring carbon atoms T h e d e s h i e l d i n g i n f l u e n c e o f a d o u b l e b o n d is n o t c o n f i n e d to t h e a d j a c e n t (allylic) c a r b o n a t o m b u t s h o w s i t s e l f at a r e d u c e d level f o r a t l e a s t 5 c a r b o n a t o m s . T h e s e
Table 4A Chemical shift (ppm) for allylic carbon a t o m s unaffected by CO2H or Ctt 3 groups.
- C H = CHCH2-(trans) - C H = CHC_H2-(cis)
acids esters
Mean value
No. of examples
32.67 a
15
27.30 b 27.35 c
23 9
- C H = CH_CH2CH = C H -
(c, c) (c,t) , (t, t )
25.72 30.56 35.68
10 1 1
-CH = CHCH2C~ C -
(c, a) ( t , a)
17.24 22.07
1 1
(c_, c) (c, c) (c, c) (c, c) (t, t)
27.37, 27.54 26.95 27.21 27.29 32.08
2 2 2 1 1
- C H = CHCH2(CH2)nCH2CH = CH n =0 1 2 3 3 a Range 32.64 - 32.69. b Range 27.22 - 2 7 . 3 9 . c Range 27.21 --27.43.
C ( n - 1) C(_n + 2)
nd
24.78
nd nd
32.77 27.48
nd nd
22.66 . .
31.91 -
26.54 . .
32.21 -
26.86
~6
32.40
27.07
~7
~8
C ( w + 2) C(co - 1)
3 2 . 5 8 C ( t o + 2) C(eo - 1)
-
32.36
27.01
34.81
29.71
~4
25.67
27.15 20.60
w3
32.51 17.87
26.83 12.72
w2
A d a s h i n d i c a t e s e i t h e r t h a t t h e r e is n o v a l u e t o b e m e a s u r e d o r t h a t t h e c h e m i c a l shift h a s t h e n o r m a l value g i v e n in t a b l e 4 A . n d = n o t d e t e r m i n e d .
C ( n - 1) C ( n + 2)
Trans-alk enes
Cis-alk enes
~5
w5
44
42
43
Acids/esters
Acids only
C h e m i c a l shift ( p p m ) f o r allylic c a r b o n a t o m s also a f f e c t e d b y C O 2 H o r C H 3 g r o u p s .
T a b l e 4B
nd -
33.89 -
~1
F.D. Gunstone et al., 13C-NMR studies o f olefinic acids
127
Table 5 Changes in chemical shift of CH 2 groups (29.80 in acids and 29.84 in esters) produced by cis and trans double bonds.
Cis Trans
c~
~
y
6
e
-2.50 + 2.85
-0.05 -0.10
0.45 -0.55
-0.20 -0.20
0.10 0.10
changes have the general values s h o w n in table 5 b u t m a y be s o m e w h a t d i f f e r e n t for c a r b o n a t o m s lying b e t w e e n the double b o n d and an end group w h e n t h e y are close together. Nor do t h e y apply to the vinyl group (CH2 = C H - ) or to A2 alkenoic acids/ esters. A p a r t f r o m the e f f e c t on the allylic c a r b o n a t o m the c o n f i g u r a t i o n o f the Table 6 Chemical shifts (ppm) of carbon atoms between two cis double bonds, n 5 4 3 2
Chemical shifts 27.29 27.20 26.95 { 27.37 27.54
29.72 29.45 29.89 27.37 27.54
29.04 29.45 26.95
C(2) C(3) C(4) C(5) C(6)
29.72 27.20
one example two examples two examples
27.29
two examples
Table 7 Average chemical shifts (ppm) in the C(2) of cis olefinic acids.
wl 0)2 co3 co4
CH = CH(CH2)nCH = CH
C(6) and oA-oa4 carbon atoms derived from a series
Sat t
col (2)
to2 (2)
w3 (3)
to4 (2)
co5 (3)
w6 (15)
to7 (6)
0o8 ** (4)
14.12 22.79 32.06 29.49
* * 33.9 29.3
12.7 * * 26.8
14.4 20.6 * *
13.8 23.0 29.7 *
14.0 22.4 32.0 27.0
14.1 22.6 31.6 29.4
14.1 22.7 31.9 29.1
14.1 22.7 32.0 29.3
A2 (1)
A3 (4)
A4 (3)
A5 (6)
A6 (8)
A7 (6)
A8 (5)
A9 (3)
A10 (1)
* * 24.8 29.3 29.2
32.9 * * 27.5 29.5
34.3 22.7 * * 27.3
33.6 24.7 26.5 * *
34.1 24.4 29.2 26.9 *
34.2 24.7 28.9 29.4 27.1
34.2 24.8 29.1 29.0 29.6
34.2 24.8 29.2 29.2 29.2
34.2 24.8 29.2 29.4 29.4
34.23 24.80 29.22 29.38 29.56
These values relate to the alkanoic acid and are to be compared with the listed values observed for the alkenoic acids. * The chemical shifts of olefinic carbon atoms are not recorded. ** Double bond position and number of examples.
128
F.D. Gunstone et al., 13C-NMR studies of olefinic acids
double bond has only a minor effect on the remaining deshielding influences. The effect of the double bond is less than that of the triple bond [2]. Methylene groups between two double bonds come under the influence of both and the results (summarised in table 6) are not very different from those expected from smnming the appropriate values from table 5. The carbon atoms at each end of a long-chain acid (A1--3 and col - 3 ) have such distmctive signals that they are easily recognised even when shifted slightly from their usual values. Typical values for cis olefinic acids (table 7) indicate that a cis unsaturated centre is easily recognised in positions A2 and A9 and col to co8. The limited results for the trans acids indicate similar discrimination. These values are particularly useful when examining polyenoic acids for these are likely to have a double bond near to one or both ends of the molecule and in these cases the double bond position is not immediately obvious from the chemical shift of the olefinic carbon atoms.
III.
Experimental
The olefinic acids were available from previous synthetic programmes [ 9 - 1 2 ] or by partial hydrogenation o f the acetylenic acids [13] kindly supplied by N.W. Gilman and B.C. Holland (Hoffinan-La Roche, New Jersey) for our previous studies [2]. The spectra were run on a Varian CFT-20 13C-NMR spectrometer using 1 M solutions in CDC13 (10 mm tubes) with TMS as internal standard. The spectra are noise decoupled and were run in the range 0 - 2 0 0 ppm and, in some cases, 0 - 4 0 ppm to give an expansion of the 29 ppm region.
Acknowledgements We acknowledge assistance from the Science Research Council (MRP and CMS) and from the British Council and the University of St. Andrews (HSV) and thank Mrs. M. Smith for technical assistance in obtaining the spectra.
References [1] D.J. Frost and F.D. Gunstone, Chem. Phys. Lipids 15 (1975) 53 [2] F.D. Gunstone, M.R. Pollard, C.M. Scrimgeour, N.W. Gilman and B.C. Holland, Chem. Phys. Lipids 17 (1976) 1 [3] W. Stoffel, O. Zierenberg and B.D. Tunggal, Z. Physiol. Chem. 354 (1972) 1962 [4] J.G. Batchelor, J.M. Prestegard, R.J. Cushley and S.R. Lipsky, J. Am. Chem. Soc. 95 (1973) 6358 x" [5] J.E. Cronan, Jr. and J.G. Batchelor, Chem. Phys. Lipids 11 (1973) 196 [6] J.G. Batchelor, R.J. Cushley and J.H. Prestegard, J. Org. Chem. 39 (1974) 1698
F.D. Gunstone et al., 13C-NMR studies o f olefinic acids
129
[7] J. Bus and D.J. Frost, Recl. Tray. Chim. Pays-Bas 93 (1974) 213; in: R. Paoletti, G. Jacini and R. Porcellati (Eds.), Lipids, Vol. 2, Technology, Raven Press, New York (1976) p. 343 [8] P.G. Barton, Chem. Phys. Lipids 14 (1975) 336 [9] F.D. Gunstone and I.A. Ismail, Chem. Phys. Lipids 1 0 9 6 7 ) 209 [10] J.A. Barve and F.D. Gunstone, Chem. Phys. Lipids 7 (1971) 3 l l [ 11 ] F.D. Gunstone and M. Lie Ken Jie, Chem. Phys. Lipids 4 (1970) 1 [12] F.D. Gunstone, M.R. Pollard and H.S. Vedanayagam, unpublished observations [13] N.W. Gilman and B.C. Holland, Chem. Phys. Lipids 13 (1974) 239 [14] A.P. Tulloch and M. Mazurek, Lipids 1l (1976) 228
FATTY ACIDS. PART 50 *. 13C NUCLEAR MAGNETIC RESONANCE STUDIES OF OLEFINIC FATTY ACIDS AND ESTERS F.D. GUNSTONE, M.R. POLLARD, C.M. SCRIMGEOUR and H.S. VEDANAYAGAM Department of Chemistry, University of St. Andrews, Fife KY16 9ST, Scotland Received May 4th, 1976,
accepted August 4th, 1976
The 13C-NMR spectra of 48 cis alkenoic acids and esters (C8-C20), 18 trans alkenoic acids and esters ( C 9 - C 1 8 ) , and 26 polyenoic acids and esters (C18-C22) are reported and interpreted. The characteristic features of such spectra which permit structural assignments to be made are discussed.
I. Introduction Our study of the IH-NMR spectra of alkenoic and alkynoic acids and their derivatives [ 1] is being followed by a similar study of their 13C-NMR spectra and we have 'already reported on a range of saturated acids and esters and on 47 acetylenic acids [2]. In this paper we describe a similar study of olefinic acids and esters containing 1 - 4 cis double bonds, acids and esters with one trans double bond, and acids and esters with mixed unsaturation. Information on compounds of this type has already been reported by Stoffel et al. [3], Batchelor et al. [4], Cronan and Batchelor [5], Batchelor et al. [6], Bus and Frost [7], Barton [8] and Tulloch and Mazurek [14] who have drawn attention to the very distinctive signals associated with the olefinic, allylic, A1--3, and w l - 3 carbon atoms. Building on these results and making use of our data on the shorter chain acids (C8-C14) we have made a careful study of deshielding influences.
I1. Results and discussion Our results are set out in table 1. The allocation of chemical shifts is based on information available in the published work already listed and on the assumption that the influence of a functional group on the chemical shift of neighbouring carbon atoms is consistent through a range of structures. Chemical shifts are given to two
* Fatty Acids. Part 49. J. Sci. Food Agric. 27 (1976) 675. 115
116
F.D. Gunstone et al., 13C-NMR studies of olefinic acids
decimal places as obtained from the spectrometer and are considered to be reproducible to -+0.05 p p m . For a few o f the molecules the n u m b e r of signals is the same as the n u m b e r of carbon atoms and the allocation of resonances to individual carbon atoms is then not difficult. When the n u m b e r of signals is less than the n u m b e r of carbon atoms assignment is m o r e difficult (and in a few cases may even be in doubt). Also the chemical shifts for i n c o m p l e t e l y resolved signals are likely to be less accurate than w h e n a shift applies to a single carbon atom. Peak heights for one-carbon signals are n o t always identical and it is difficult to assign the correct n u m b e r of carbon atoms to overlapping resonances from peak heights alone. A. Olefinic carbon atoms in m o n o e n o i c acids and esters O f the 66 cis and trans m o n o e n o i c acids and esters listed in table l all except 6 show two resonances for their olefinic carbon atoms. These are the 17 : 1 12c (129.89) and 20 : 1 1 l e (129.88) m e t h y l esters, the 18 : 1 12c (129.94) and 18 : 1 13c (129.90) acids, and the 18 : 1 12t (130.41) and 18 : 1 13t (130.39) acids. The mean values o f Table 1 Allocation of resonance signals (ppm downfield from Me4Si) for olefinic acids and esters. Table 1A. C 8-C14 cis alkenoic acids. C(1) 8: 1(7) 10: 1(8) 11 : 1(4) (5) (6) (8) (10) 12: 1(3) (5) (7) (10) 13 : 1(3) (5) (6) (7) (9) (10) 14 : 1 (3) (4) (5) (6) (7) (8)
180.64 180.54 180.01 180.50 180.42 180.59 180.34 178.51 180.44 180.46 180.53 178.48 180.15 180.41 180.58 180.53 180.66 178.68 180.00 180.46 180.30 180.39 180.63
C(2) 34.16 34.18 34.35 33.58 34.09 34.21 34.19 32.78 33.56 34.20 34.18 32.8l 33.55 34.09 34.18 34.18 34.22 32.73 34.35 33.55 34.08 34.22 34.20
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
24.59 24.71 22.66 24.74 24.39 24.75 24~76 120.01 24.71 24.69 24.73 120.09 24.72 24.37 24.67 24.73 24.76 120.04 22.65 24.70 24.37 24.70 24.75
28.59 29.00 127.04 26.55 29.02 29.04 29.16 134.21 26.53 28.79 29.14 134.17 26.52 29.17 28.79 29.12 29.30 134.14 127.04 26.53 29.28 28.80 29.04
28.59 28.92 131.94 128.23 26.86 28.94 29.28 27.48 128.20 29.42 29.14 27.49 128.19 26.85 29.44 29.12 29.30 27.47 131.93 128.19 26.85 29.42 28.99
33.61 29.36 27.30 131.44 129.04 29.60 29.28 29.31 131.42 27.03 29.14 29.36 131.44 129.03 27.05 29.12 29.30 29.33 27.30 131.43 129.01 27.05 29.59
138.71 26.77 29.69 27.29 130.57 27.07 29.16 29.31 27.32 129.48 29.14 29.36 27.3l 130.63 129.46 29.73 29.30 29.33 29.70 27.32 130.64 129.44 27.22
114.53 130.67 29.05 29.46 27.01 129.11 29.00 29.31 29.73 130.29 29.14 29.58 29.75 27.32 130.33 27.24 29.83 29.65 29.44 29.75 27.32 130.29 129.64
F.D. Gunstone et al., 13C-NMR studies of olefinie acids
117
129.90 (cis) and 130.40 (trans) compare with values of 29.84 and 29.80 for undisturbed CH 2 groups in long-chain esters and acids respectively [2]. The two signals corresponding to the olefinic carbon atoms of the remaining monoenes have been allocated on the basis of values previously recorded [3,4,6-8] and particularly on the results of Cronan and Batchelor [5] who confirmed the allocation for 16 : 1 9c by the study of esters produced biosynthetically from 13C-labelled acetate. Our results show that olefinic carbon atoms are influenced by a COOH or COOMe group up to A10 or A11 or by the end methyl group up to w4 and, in appropriate shortchain compounds, by both influences in an additive manner. The chemical shifts for cis and trans olefinic carbon atoms in long-chain acids/esters are listed in table 2. The 11 : 1 8c and 13 : 1 9c acids are representative of compounds in which olefinic carbon atoms are influenced by both COOH and CH3 groups: the observed shifts are very close to those calculated from the information given in table 2. 11 : 1 8 c ( w 3 ) 13 : 19c(6o4)
C(8) C(9) C(9) C(10)
129.90-0.25-0.53= 129.12 129.90 + 0.25 + 1.63 = 131.78 129.90-0.11 +0.23=130.02 129.90 + 0.15 - 0.25 = 129.80
C(I1)
C(12)
C(13)
C(14)
14.13 14.08 13.99 12.72 22.74 22.71 22.70 22.64 22.95 20.60 31.97 32.03 31.98 31.93 31.85 31.65
14.11 14.08 14.08 14.08 13.79 14.40 22.73 22.73 22.74 22.72 22.71 22.67
14.10 14.12 14.10 14.10 14.08 14.07
C(9)
C(IO)
123.83 31.87 31.6l 32.01 131.78 33.86 29.31 29.05 27.03 26.89 29.63 29.29 29.76 27.27 130.00 27.16 29.65 29.70 29.40 29.79 27.30 130.14
12.71 22.66 14.10 22.64 14.06 2 2 . 4 1 13.98 20.60 14.38 139.04 114.24 3 1 . 8 9 22.73 3 1 . 8 4 22.71 3 2 . 0 4 22.40 130.83 1 2 3 . 6 5 29.36 31.98 29.29 31.93 29.08 31.85 29.44 31.62 1 2 9 . 7 9 29.73 129.29 1 3 1 . 6 2 29.65 29.33 29.70 29.44 29.58 29.40 29.28 29.28 29.79 29.05 27.22 29.59
obs. obs. obs. obs.
129.11 131.78 130.00 129.79
118
F.D. Gunstone et al., 13C-NMR studies of olefinic acids
Table lB. C16 C20 cis alkenoic acids and esters.
16: 1(8)* 17 : 1(12)* 18:1(2) (2)* (3) (3) * (4) (4)* (5) (5)* (6) (6)* (7) (7)* (8) (9) (9)* (10) (11) (12) (13) (14) (15) (17) 2 0 : 1 (11)*
C(1)
C(2)
174.26 a 174.06 b . . . 166.53 c 178.52 172.08 d 180.04 173.10 e 180.45 173.81 f 180.51 173.57 g 180.30 173.87 h 180.54 180.55 J 180.46 180.55 i80.53 180.54 180.58 180.61 180.63 173.93 k
34.14 34.14 . 119.41 33.12 32.80 34.27 34.21 33.58 33.48 34.13 33.98 34.22 34.08 34.22 34.24 34.12 34.22 34.22 34.31 34.18 34.25 34.23 34.21 34.t2
C(3) 25.01 25.06 150.69 120.55 121.00 22.66 22.98 24.74 25.05 24.39 24.76 24.73 25.00 24.78 24.80 25.08 24.81 24.76 24.82 24.74 24.78 24.79 24.78 25.08
C(4)
C(5)
C(6)
C(7)
C(8)
29.14 28.97 29.62 27.21 29.39 29.39 29.63 29.63 24.78 + 29.34 29.17 29.74 29.61 * 29.13 * 29.26 4 29.90 133.76 27.49 29.46 29.46 133.40 27.54 29.55 29.90 127.09 131.99 27.33 29.79 127.53 131.54 27.35 29.91 26.58 128.21 131.44 27.36 26.69 128.44 131.21 27.37 29.23 26.88 129.01 130.62 29.51 27.02 129.18 130.48 28.88 29.51 27.13 129.45 28.95 29.51 27.14 129.49 29.08 28.96 29.48 27.28 29.22 29.22 29.22 29.83 29.28 29.28 29.28 29.83 29.22 29.35 29.35 29.35 29.17 29.32 29.49 29.49 29.40 29.40 29.56 29.56 29.16 29.34 29.64 29.81 29.17 29.40 29.69 29.69 29.21 29.39 29.57 29.75 29.19 29.32 29.75 29.75 29.38 29.45 29.45 29.58
129.68 29.63 29.74 29.90 29.78 29.90 29.48 29.57 29.81 29.83 27.36 27.43 130.31 130.22 129.65 27.31 27.32 29.85 29.32 29.56 29.64 29.69 29.75 29.75 29.38
Esters. * Assignments uncertain (see text). Also signals at: 51.38 (a), 51.27 (b), 50.71 (c), 51.56 (d), 51.21 (e), 51.25 (f), 51.56 (g), 51.22 (h), 51.21 (j), 51.22 (k), 22.80 and 14.12 (1).
Our results suggest t h a t for m o n o e n e acids o f esters o f k n o w n c h a i n - l e n g t h ( a n d s o m e t i m e s w h e n t h e c h a i n - l e n g t h is n o t k n o w n ) the c h e m i c a l shift o f t h e olefinic c a r b o n a t o m s is sufficient to s h o w w h e t h e r the d o u b l e b o n d has cis or trans configur a t i o n and to i n d i c a t e its p o s i t i o n e x c e p t in those few c o m p o u n d s w h e r e only o n e olefinic signal is o b s e r v e d [7,8].
B. Olefinic carbon atoms in polyunsaturated acids and esters T h e diene acid/ester s p e c t r a c o n t a i n 4 signals c o r r e s p o n d i n g to u n s a t u r a t e d carb o n a t o m s . We assume t h a t each olefinic c e n t r e m a y be i n f l u e n c e d b y the acid (ester) group, t h e e n d m e t h y l , a n d the s e c o n d d o u b l e b o n d in an additive m a n n e r , and we
P2D. Gunstone et al., 13C-NMR studies o f olefinie acids
119
c(9)
C(10)
C(ll)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
130.13 29.39 29.74 29.90 29.78 29.90 29.79 29.91 29.48 29.51 29.76 29.93 27.39 27.36 130.17 129.78 129.78 27.30 29.82 29.40 29.64 29.69 29.75 29.75 29.90
27.21 29:87 29.74 29.90 29.78 29.90 29.79 29.91 29.81 29.83 29.45 29.59 29.81 29.82 27.28 130.09 130.02 129.83 27.29 29.56 29.34 29.69 29.75 29.75 27.34
29.84 27.30 29.74 29.90 29.78 29.90 29.79 29.91 29.81 29.83 29.76 29.93 29.51 29.51 29.70 27.31 27.32 130.00 129.89 27.29 29.81 29.40 29.57 29.75 129.88
29.31 129.89 29.74 29.90 29.78 29.90 29.79 29.91 29.81 29.83 29.76 29.93 29.81 29.82 29.48 29.83 29.90 27.30 129.96 129.94 27.27 29.69 29.39 29.75 129.88
29.31 129.89 29.74 29.90 29.78 29.90 29.79 29.91 29.81 29.83 29.76 29.93 29.81 29.82 29.70 29.47 29.46 29.85 27.29 129.94 129.90 27.33 29.75 29.75 27.34
31.95 27.01 29.74 29.90 29.78 29.90 29.79 29.91 29.81 29.83 29.76 29.93 29.81 29.82 29.70 29.68 29.68 29.35 29.82 27.29 129.90 130.16 27.21 29.25 29.90
22.72 32.09 29.46 29.61 29.46 29.55 29.51 29.57 29.48 29.5l 29.45 29.59 29.51 29.51 29.48 29.47 29.46 29.35 29.08 29.40 26.99 129.66 129.39 29.09 29.38
14.10 22.42 32.03 32.15 32.04 32.15 32.06 32.17 32.06 32.10 32.04 32.18 32.10 32.08 32.06 32.06 32.07 32.01 31.87 31.64 32.06 29.69 131.54 33.91 29.58
14.0l 22.76 22.86 22.78 22.88 22.75 22.91 22.79 22.83 22.78 22.89 22.82 22.81 22.80 22.80 22.79 22.76 22.72 22.68 22.40 22.96 20.60 139.13 29.46
14.12 14.15 14.13 14.17 14.13 14.16 14.13 14.14 14.11 14.18 14.13 14.12 14.12 14.13 14.11 14.12 14.10 14.09 14.00 13.80 14.41 114.15 32.071
use t h e results in table 2 to find values for the i n f l u e n c e o f o n e d o u b l e b o n d o n ano t h e r b y selecting those t h a t give the best fit. These i n f l u e n c e s are c o n v e n i e n t l y repr e s e n t e d b y greek letters, thus:
-CH ~3'
= CHCH2CH = CH/3
a
- CH = C H C H z C H z C H 2 C H = C H - . 6'
6
3'
/3
a
Consider, as an e x a m p l e , the 8c 12c a n d 6c 10c C18 diene acids. T h e c h e m i c a l shift o f each olefinic c a r b o n a t o m is given b y C(8) C(9) C(12) C(13)
129.90 129.90 129.90 129.90
+ + +
0.25 + 7 ' 0.25 + 3' 3' 3''
C(6) C(7) C(10) C(11)
129.90 129.90 129.90 129.90
+ +
0.88 0.72 0.07 0.10
+ + + +
3" 3' 3' 3''
120
F.D. Gunstone et al., 13C-NMR studies o f olefinic acids
Table 1C. C 9 C18 trans alkenoic acids and esters. C(1) 9 : 1(7) 10 : 1 (7)* (8)* 12 : 1(8)* 16:1 (7)* (8)* 18 : 1(5) (6) (7) (7)* (8) (9) (10) (11) (12) (13) (14) (15)
174.16 m 174.06 n 174.08 p 174.09 q 173.89 r 173.86 s 180.58 180.51 180.53 173.65 t 180.43 180.61 180.62 180.57 180.57 180.59 180.59 180.57
C(2) 34.12 34.12 34.13 34.13 34.10 34.12 33.47 34.06 34.20 34.06 34.20 34.19 34.21 34.22 34.20 34.21 34.21 34.21
C(3) 24.94 24.95 25.04 25.05 24.97 25.09 24.57 24.22 24.63 24.99 24.74 24.75 24.76 24.77 24.77 24.77 24.78 24.78
C(4)
C(5)
C(6)
2 8 . 7 5 29.29 32.42 2 8 . 7 5 2 9 . 3 5 32.42 29.14 28.88 29.50 29.15 28.86 29.55 28.79 29.39 32.50 2 9 . 2 1 28.92 29.62 31.91 128.72 131.98 29.07 3 2 . 2 1 129.49 28.63 29.31 32.40 28.83 29.43 32.55 29.02 28.79 29.46 29.14 29.17 29.00 29.18 29.30 29.40 29.20 29.32 29.53 29.17 2 9 . 3 1 29.53 29.20 29.34 29.55 29.18 29.32 29.54 29.18 2 9 . 2 8 29.53
C(7)
C(8)
131.34 129.05 32.60 32.62 130.01 32.61 32.65 131.13 129.89 130.03 32.58 29.65 29.18 29.53 29.64 29.70 29.71 29.73
124.89 132.26 131.52 130.41 130.75 130.21 29.66 32.67 130.81 130.75 130.13 32.64 29.75 29.20 29.55 29.70 29.71 29.73
* Esters. Also signals at: 51.35 (m), 51.31 (n), 51.31 (p), 51.29 (q), 51.24 (r), 51.21 (s), 51.15 (t). These are fitted to the observed values in ways which give the most consistent values for 3"(+0.43, +0.51, +0.46, +0.51) and 3'( 0.71, - 0 . 7 1 , - 0 . 7 3 , - 0 . 7 5 ) . Average values obtained in this way from several dienes are listed in table 3. Similar values were reported previously [6] for/3 a n d / 3 ' ( - 1.83 and +0.30), y and 3"( 0.5 and +0.5), and c and e ' ( - 0 . 2 8 and +0.23). Of the dienes we examined only linoleic acid has been reported before. Our assignments agree with those of Batchelor et al. [6] but differ from those of Stoffel et al. [3]. In a similar examination of our 6 triene acids/esters values of/3 and/3' obtained from the dienes are used and values of e* and e*' are derived (see table 3). The symbol e* refers to the effect of the double bond on an olefinic carbon atom operating through another double bond and is not necessarily identical with the value e which does not operate through a double bond. The chemical shifts of the inner pair of olefinic carbon atoms depend only on/3 and/3' and the shifts observed in the trienes agree well (average +0.03 for 12 values) with those calculated on the basis of the and/3' values derived from the dienes. For the remaining 4 olefinic carbon atoms in each triene account must also be taken of values for e* and e*' and these are again selected to give the best fit between observed and calculated values. Although these are internally consistent the values from the two eo3 trienes differ slightly from those from the 4 6o6 trienes and the average values are quoted separately in table 3. It is not clear why these values should differ. The 6o3 values for e* and e*' hardly differ
F.D. Gunstone et al., 13C-NMR studies of olefi'nic acids
C(9)
C(10)
C(ll)
C(12)
C(13)
C(14)
17.87 25.68 124.75 130.41 32.74 130.64 29.30 29.75 32.67 32.79 130.67 130.23 32.68 29.73 29.21 29.63 29.71 29.73
14".01 17.87 34.83 29.81 32.76 29.66 29.30 29.76 29.87 32.68 130.54 130.31 32.69 29.72 29.27 29.54 29.73
22.85 13.65 29.39 29.67 29.39 32.09 29.87 29.35 29.35 32.09 29.78 29.78 29.78 29.78 29.67 29.75 29.75 29.75 2 9 . 3 1 29.65 29.76 29.76 29.43 29.87 29.87 29.87 29.72 29.28 29.72 29.72 32.66 29.76 29.28 29.60 130.47 32.68 29.75 29.26 130.35 130.43 32.69 29.73 32.65 130.41 1 3 0 . 4 1 32.65 29.76 32.69 130.39 130.39 29.26 2 9 . 7 1 32.69 130.63 29.53 29.28 29.73 32.65
C(15)
C(16)
22.83 22.84 29.47 29.45 29.45 29.58 29.46 29.4l 29.30 28.93 29.43 32.36 130.13 129.45
14.14 14.14 32.04 32.04 32.05 32.15 32.01 32.01 32.00 31.88 31.49 31.96 34.79 131.93
121
C(17)
22.78 22.76 22.78 22.87 22.76 22.76 22.77 22.73 22.62 22.27 22.82 25.65
C(18)
14,12 14.12 14.11 14.15 14.ll 14.11 14.11 14.10 14.07 13.96 13.64 14.04
from the e and e' values derived from the 18 : 2 (6, 12) and 20 : 3 (7, 13) dienes. For the two tetraenes examined (20 : 4 6o6 and 22 : 4 6o6) the/3 and/3' values from the dienes and the e* and e*' values from the 6o6 trienes are used. Again chemical shifts involving only these values give a good agreement between observed and calculated values (average of-+0.06 for 8 values). There is no difficulty in assigning the observed chemical shifts to the remaining olefinic centres in each compound but the 0"* and 0"*' values are less consistent than usual (see footnote to table 3). Table 3 also contains some values for systems other than all-cis polyenes. Cis and trans double bonds seem to exert a similar but not identical effect on each other whereas in the enynes examined the chemical shift induced in a triple bond by a nearby double bond differs markedly from the shift induced in the sp 2 carbon atoms by the triple bond. C. Allylic carbon atoms In a monoenoic acid or ester there is an easily recognised signal associated with the allylic carbon atoms. When not also influenced by CO2 H or CH3 end groups, this lies in the range 2 7 . 2 2 - 2 7 . 3 9 (mean 27.30) for a cis double bond and in the range 3 2 . 6 4 - 3 2 . 6 9 (mean 32.67) for a trans double bond. These values differ from each other and from the propargylic carbon atoms (18.85) reported in our earlier paper [2]. Different values are observed (tables 4A and 4B) when the allylic atom is also influenced by a COOH or CH 3 group or by a second double bond and these values are frequently of diagnostic value for recognising the position of unsaturated centres.
F.D. Gunstone et al., 13C-NMR studies of olefinic acids
122
Table ID. C18, C19 , C20 and C22 polyunsaturated acids and esters. C(1) All cis isomers 1 8 : 2 ( 5 , 12) (6,9) (6, 10) (6,11) (6, 12) (7, 12) (8, 12) (9, 12) 20 : 2(7, 13) (11,14)* All cis isomers 18:3(6,9,12)4 (6,9,12)* (9, 12, 15) 19: 3(7, 10, 13)* 20 : 3 (8, 11,14) (8,11,14)**
(11,14, 17)* 20:4(5,8,11,14)* 22:4(7,10,13,16) Other polyunsaturated 18 : 2(9t 12t)* (7t 12t)* (9c12t)* (9c 12t)* ~ (9t 12c) *s (9a12c)* (9c12a)* (9t 12a)* (9c12a 14c)*
C(2)
180.29 180.29 180.28 180.31 180.31 180.46 180.42 180.56 180.48 174.06 v
33.56 34.15 34.14 34.09 34.09 34.17 34.18 34.22 34.24 34.13
173.83 180.39 174.03 179.87 173.44 173.98 174.13 174.19 173.84 180.16
. 33.99 34.19 34.07 34.04 34.03 34.08 34.12 34.12 34.11 33.50 34.07
x y b' d' f' h' k' m
t
C(3)
C(4)
C(5)
C(6)
'C(7)
C(8)
26.56 29.14 29.21 29.20 29.22 28.80 29.08 29.21 28.82 29.38
128.29 26.90 26.91 26.95 26.89 29.41 29.00 29.21 29.44 29.47
131.29 129.29 129.48 129.34 129.13 26.95 29.56 29.21 27.18 29.55
27.29 128.74 129.89 130.28 130.41 129.73 27.32 29.72 129.54 29.55
29.' 25.' 27.1 26.! 27.~ 129.! 130.1 27.Z 130.~ 29.:
24.70 24.79 24.92 24.66 25.08 25.00 24.99 24.98 25.10 24.89 24.63
. 29.23 29.23 28.85 28.92 29.11 29.00 28.96 28.95 29.35 26.65 28.75
. 26.96 29.23 29.34 28.92 29.25 29.14 29.11 29.12 29.42 128.96 29.29
. 129.60 29.23 27.09 29.38 29.63 29.46 29.47 29.45 29.42 128.96 27.07
128.38 29.72 129.96 27.23 27.37 27.27 27.25 27.24 29.62 25.71 130.00
25.' 272 128.1 130. 130.( 130.1 130. 130. 29.: 128." 128.(
24.74 24.43 24.40 24.40 24.38 24.66 24.75 24.78 24.74 25.05
.
.
esters 174.15 q' 174.26 r' 174.08 s'
34.12 34.12 34.12
25.02 24.89 25.04
29.18 28.69 29.23
29.18 29.32 29.23
29.04 32.41 29.23
29.52 130.25 29.68
173.81 t'
34.07
25.08
29.28
29.28
29.28
29.70
32..' 130.~ 27.1 ~-27.: ~32.f
173.97 174.20 174.01 173.91
34.08 34.12 34.09 34.07
25.02 25.01 25.05 25.04
29.15 29.17 29.23 29.23
28.91 29.17 29.23 29.23
28.77 29.17 29.12 29.23
29.15 29.38 29.39 29.39
18A 27.] 32.: 27S
u' v' w' x'
* Esters. ** Methyl esters at 2 M, 1 M, 0.4 M, and 0.14 M concentration respectively. Hydrocarbon. Carbon atoms 1 - 9 have the same chemical shifts as carbon atoms 1 8 - 1 0 respectively. They are presented in this way to emphasize their similarity to acids/esters at the CH 3 end. Also signals at: 22.72 and 14.10 (u), 51.29 (v), 22.67 and 14.10 (w), 51.31 (x), 51.35 (y), 14.05 (z), 22.58 and 14.03 (a'), 51.08 (b'), 22.76 and 14.11 (c'), 51.29 (d'), 22.66 and 14.07 (e'), 51.36 (f'), 22.62 and 14.06 (g'), 51.39 (h'), 22.58 and 14.03 (j'), 51.19 (k'), 20.67 and 14.30 (1'), 51.40 (m'), 22.61 and 14.05 (n'), 29.29, 31.57, 22.60 and 14.05 (p'), 51.32 (q'), 51.39 (r'), 51.29 (s'), 51.19 (t'), 51.28 (u'), 51.36 (v'), 51.27 (w') and 51.26 (x').
F.D. Gunstone et al., 13C-NMR studies o f olefinic acids
C(9)
C(IO)
C(ll)
C(12)
C(13)
C(14)
C(15)
29.04 127.82 27.37 29.85 29.45 26,95 129,44 130,01 27,18 29.76
29.72 130.34 129.08 26.95 29,45 29.92 27.54 128,24 29.44 27.32
27.29 27.33 130.51 129.49 27.21 26.95 27.54 25.77 29.44 130.13
129.81 29.75 27.37 130.28 129.70 129.53 129.19 128.08 27.18 128.07
130.02 29.41 29.83 27.34 130.07 130.29 130.41 130.20 129.71 25.74
27.29 29.62 29.33 29.85 27.21 27.28 27.32 27.32 130.08 128.07
29.58 29.4l 29.33 29.11 29.45 29.41 29.56 29.48 27.18 130.13
31.64 32.00 31.97 31.92 31.63 31.60 31.64 31.67 29.82 27,32
22.68 22.75 22.74 22.75 22.67 22.64 22.69 22.69 29.06 29,49
128.14 130.17 25.71 127.94 128.07 127.96 127.93 127.91 29.82 128.25 25.71
128.37 128,46 127.94 128.19 25.68 25.80 25.73 25.71 25.70 27.37 25.71 128,41
25.77 25,74 25.76 128.39 128.26 128.28 128.28 128.27 128.27 130.28 127,97 128.01
127.81 127.74 128.33 25.71 128.38 128.36 128.36 128.36 128.39 127.87 128.65 25.71
130.41 130.42 128,33 127,71 25,68 25,80 25.73 25,71 25,70 25.75 25.71 128,01
27.34 27.33 25.68 130.40 127.71 127.88 127.75 127.73 127.71 128.33 127.63 128.59
29.46 29.44 127.28 27,27 130.43 130.27 130.36 130.41 130,44 128.33 130.51 25.71
31.66 31.64 131,88 29.34 27.20 27.37 27.27 27.25 27.24 25.71 27.29 127.64
22.66 22.66 20.68 31.58 29.38 29.56 29.46 29,47 29.45 127.31 29.39 130.50
14,06 14.07 14.31 22.62 31.55 31.74 31.63 31.59 31.59 131.86 31.59 27.27
130,92 32.08 130.31
128,79 29.62 127.94
35.68 32.08 30.55
128.65 130.08 128.40
131.08 130.72 130.84
32.59 32.62 32.64
29.18 29.32 29.23
31.50 31.47 31.53
22.60 22.59 22.64
14.06 14.07 14.08
130.27 130.64 79.79 131.14 131.59 131,54
127.96) 128.59 78.51 125.28 125.09 124.60
30,56
,f128.45 "127.83 125.28 78.40 77.62 92,37
22,69
14.10
22.66 22,29 22.35 22.27
14.07 14.00 14.02 13.76
-
17.24 17,24 22.07 18.02
130.79 32.67) 1 3 ( ) . 4 1 27.22 131.19 27.17 80.08 18.83 81.96 18.88 77.24 142.28
29.28 29.15 28.85 28.96 109.76
C(16)
123
~-31,59], "31.65 ~ 31.59 31.18 31.23 32.15
C(17)
C(18) 14.09 14.11 14.10 14,12 14.08 14.06 14.10 14.08 31.88 u 31.65 w
z a' c' e' ,gl J 1' n' P'
-9.85, -2.84, -1.70, -0.88, 0.44, 0.25, -0.11, -0.07, -0.01, +1.01, 0.53, +0.23,
+4.27(3) +2.05(2) +1.53(5) +0.72(4) +0.41(4) +0.25(2) +0.15(3) +0.10 +0.06 -6.33(2) +1.63(3) - 0 . 2 5 (2)
+20,79 + 3.50 + 1.64 + 1.31 + 0.58 + 0.32 + 0.23 + 0.12 0 -
-10.49, - 8.90, - 2.37, - 1.46, - 0.72, - 0.41, 0.22, 0.12, 0 -
-1.68, -0.91, -0.31, 0.27, -0.17, 0.09, -0.05, -0.95, +0.23,
. .
. .
+1.53 -0.27
+1.58 +0.73 +0.41 +0.27 +0.14 +0.07 +0.03
. .
Acids
Acids
Esters
Trans c o m p o u n d s *
Cix c o m p o u n d s *
. .
+1.39, -0.84, +0.20,
-0.38, -0.19, -
Esters
-5.92(2) +1.45 -0.23
-
+0.35 +0.24
* T h e shifts r e f e r to c a r b o n a t o m s n a n d n + 1 f o r t h e An series a n d to c a r b o n a t o m s m + 1 a n d m f o r t h e corn series. T h e n u m b e r o f e x a m p l e s is o n e e x c e p t w h e r e o t h e r w i s e i n d i c a t e d b y t h e value in p a r e n t h e s i s . t col values (acid) are 1 3 9 . 1 2 a n d 1 1 4 . 1 5 f o r t h e col a n d w 2 c a r b o n a t o m s .
2x 2 3 4 5 6 7 8 9 10 11 co 2 ? 3 4
Position of double bond
Table 2 C h e m i c a l shift i n d u c e d in o l e f i n i c c a r b o n a t o m s ( 1 2 9 . 9 0 p p m (cis) a n d 1 3 0 . 4 0 p p m (trans) w h e n u n d i s t u r b e d ) in m o n o e n o i c a c i d s a n d esters b y COOH (COOCH3) and CH 3 groups.
a,
125
F.D. Gunstone et al., 13C-NMR studies of olefinic acids Table 3 Chemical shift induced in unsaturated carbon a t o m s by a second unsaturated system.
cis-cis ~ t3 3, ,5 e g" e*(o.,3) e*(to6)
-1.86 -0.73 -0.37 -0.21 -0.12 -0.21 -0.34
+0.26(6) +0.48(4) +0.32(4) +0.14(4) +0.11(2) +0.10(4) +0.23(8)
trans-trans
eis-trans
-1.75
+0.67(2)
-2.03
-0.32
+0.28(2)
+0.45(4)
Less concordant values were derived for 0 ** ( - 0 . 0 5 , - 0 . 0 7 , +0.02, +0.12) and 0 **' (+0.03, +0.12, +0.05, 0.06). For explanation of symbols see text. Figures in parenthesis are the n u m b e r of values which have been averaged. The two n u m b e r s relate to the unprimed and primed values respectively. * Also values for 13and/3' for cis-enyne [ - 4 . 6 8 and +1.33 (en) and - 1 . 8 1 and - 0 . 1 8 (yne)] and trans-enyne systems [ - 5 . 4 5 and +1.36 (en) and - 2 . 5 7 and +1.77 (yne)].
D. The influence o f double bonds on neighbouring carbon atoms T h e d e s h i e l d i n g i n f l u e n c e o f a d o u b l e b o n d is n o t c o n f i n e d to t h e a d j a c e n t (allylic) c a r b o n a t o m b u t s h o w s i t s e l f at a r e d u c e d level f o r a t l e a s t 5 c a r b o n a t o m s . T h e s e
Table 4A Chemical shift (ppm) for allylic carbon a t o m s unaffected by CO2H or Ctt 3 groups.
- C H = CHCH2-(trans) - C H = CHC_H2-(cis)
acids esters
Mean value
No. of examples
32.67 a
15
27.30 b 27.35 c
23 9
- C H = CH_CH2CH = C H -
(c, c) (c,t) , (t, t )
25.72 30.56 35.68
10 1 1
-CH = CHCH2C~ C -
(c, a) ( t , a)
17.24 22.07
1 1
(c_, c) (c, c) (c, c) (c, c) (t, t)
27.37, 27.54 26.95 27.21 27.29 32.08
2 2 2 1 1
- C H = CHCH2(CH2)nCH2CH = CH n =0 1 2 3 3 a Range 32.64 - 32.69. b Range 27.22 - 2 7 . 3 9 . c Range 27.21 --27.43.
C ( n - 1) C(_n + 2)
nd
24.78
nd nd
32.77 27.48
nd nd
22.66 . .
31.91 -
26.54 . .
32.21 -
26.86
~6
32.40
27.07
~7
~8
C ( w + 2) C(co - 1)
3 2 . 5 8 C ( t o + 2) C(eo - 1)
-
32.36
27.01
34.81
29.71
~4
25.67
27.15 20.60
w3
32.51 17.87
26.83 12.72
w2
A d a s h i n d i c a t e s e i t h e r t h a t t h e r e is n o v a l u e t o b e m e a s u r e d o r t h a t t h e c h e m i c a l shift h a s t h e n o r m a l value g i v e n in t a b l e 4 A . n d = n o t d e t e r m i n e d .
C ( n - 1) C ( n + 2)
Trans-alk enes
Cis-alk enes
~5
w5
44
42
43
Acids/esters
Acids only
C h e m i c a l shift ( p p m ) f o r allylic c a r b o n a t o m s also a f f e c t e d b y C O 2 H o r C H 3 g r o u p s .
T a b l e 4B
nd -
33.89 -
~1
F.D. Gunstone et al., 13C-NMR studies o f olefinic acids
127
Table 5 Changes in chemical shift of CH 2 groups (29.80 in acids and 29.84 in esters) produced by cis and trans double bonds.
Cis Trans
c~
~
y
6
e
-2.50 + 2.85
-0.05 -0.10
0.45 -0.55
-0.20 -0.20
0.10 0.10
changes have the general values s h o w n in table 5 b u t m a y be s o m e w h a t d i f f e r e n t for c a r b o n a t o m s lying b e t w e e n the double b o n d and an end group w h e n t h e y are close together. Nor do t h e y apply to the vinyl group (CH2 = C H - ) or to A2 alkenoic acids/ esters. A p a r t f r o m the e f f e c t on the allylic c a r b o n a t o m the c o n f i g u r a t i o n o f the Table 6 Chemical shifts (ppm) of carbon atoms between two cis double bonds, n 5 4 3 2
Chemical shifts 27.29 27.20 26.95 { 27.37 27.54
29.72 29.45 29.89 27.37 27.54
29.04 29.45 26.95
C(2) C(3) C(4) C(5) C(6)
29.72 27.20
one example two examples two examples
27.29
two examples
Table 7 Average chemical shifts (ppm) in the C(2) of cis olefinic acids.
wl 0)2 co3 co4
CH = CH(CH2)nCH = CH
C(6) and oA-oa4 carbon atoms derived from a series
Sat t
col (2)
to2 (2)
w3 (3)
to4 (2)
co5 (3)
w6 (15)
to7 (6)
0o8 ** (4)
14.12 22.79 32.06 29.49
* * 33.9 29.3
12.7 * * 26.8
14.4 20.6 * *
13.8 23.0 29.7 *
14.0 22.4 32.0 27.0
14.1 22.6 31.6 29.4
14.1 22.7 31.9 29.1
14.1 22.7 32.0 29.3
A2 (1)
A3 (4)
A4 (3)
A5 (6)
A6 (8)
A7 (6)
A8 (5)
A9 (3)
A10 (1)
* * 24.8 29.3 29.2
32.9 * * 27.5 29.5
34.3 22.7 * * 27.3
33.6 24.7 26.5 * *
34.1 24.4 29.2 26.9 *
34.2 24.7 28.9 29.4 27.1
34.2 24.8 29.1 29.0 29.6
34.2 24.8 29.2 29.2 29.2
34.2 24.8 29.2 29.4 29.4
34.23 24.80 29.22 29.38 29.56
These values relate to the alkanoic acid and are to be compared with the listed values observed for the alkenoic acids. * The chemical shifts of olefinic carbon atoms are not recorded. ** Double bond position and number of examples.
128
F.D. Gunstone et al., 13C-NMR studies of olefinic acids
double bond has only a minor effect on the remaining deshielding influences. The effect of the double bond is less than that of the triple bond [2]. Methylene groups between two double bonds come under the influence of both and the results (summarised in table 6) are not very different from those expected from smnming the appropriate values from table 5. The carbon atoms at each end of a long-chain acid (A1--3 and col - 3 ) have such distmctive signals that they are easily recognised even when shifted slightly from their usual values. Typical values for cis olefinic acids (table 7) indicate that a cis unsaturated centre is easily recognised in positions A2 and A9 and col to co8. The limited results for the trans acids indicate similar discrimination. These values are particularly useful when examining polyenoic acids for these are likely to have a double bond near to one or both ends of the molecule and in these cases the double bond position is not immediately obvious from the chemical shift of the olefinic carbon atoms.
III.
Experimental
The olefinic acids were available from previous synthetic programmes [ 9 - 1 2 ] or by partial hydrogenation o f the acetylenic acids [13] kindly supplied by N.W. Gilman and B.C. Holland (Hoffinan-La Roche, New Jersey) for our previous studies [2]. The spectra were run on a Varian CFT-20 13C-NMR spectrometer using 1 M solutions in CDC13 (10 mm tubes) with TMS as internal standard. The spectra are noise decoupled and were run in the range 0 - 2 0 0 ppm and, in some cases, 0 - 4 0 ppm to give an expansion of the 29 ppm region.
Acknowledgements We acknowledge assistance from the Science Research Council (MRP and CMS) and from the British Council and the University of St. Andrews (HSV) and thank Mrs. M. Smith for technical assistance in obtaining the spectra.
References [1] D.J. Frost and F.D. Gunstone, Chem. Phys. Lipids 15 (1975) 53 [2] F.D. Gunstone, M.R. Pollard, C.M. Scrimgeour, N.W. Gilman and B.C. Holland, Chem. Phys. Lipids 17 (1976) 1 [3] W. Stoffel, O. Zierenberg and B.D. Tunggal, Z. Physiol. Chem. 354 (1972) 1962 [4] J.G. Batchelor, J.M. Prestegard, R.J. Cushley and S.R. Lipsky, J. Am. Chem. Soc. 95 (1973) 6358 x" [5] J.E. Cronan, Jr. and J.G. Batchelor, Chem. Phys. Lipids 11 (1973) 196 [6] J.G. Batchelor, R.J. Cushley and J.H. Prestegard, J. Org. Chem. 39 (1974) 1698
F.D. Gunstone et al., 13C-NMR studies o f olefinic acids
129
[7] J. Bus and D.J. Frost, Recl. Tray. Chim. Pays-Bas 93 (1974) 213; in: R. Paoletti, G. Jacini and R. Porcellati (Eds.), Lipids, Vol. 2, Technology, Raven Press, New York (1976) p. 343 [8] P.G. Barton, Chem. Phys. Lipids 14 (1975) 336 [9] F.D. Gunstone and I.A. Ismail, Chem. Phys. Lipids 1 0 9 6 7 ) 209 [10] J.A. Barve and F.D. Gunstone, Chem. Phys. Lipids 7 (1971) 3 l l [ 11 ] F.D. Gunstone and M. Lie Ken Jie, Chem. Phys. Lipids 4 (1970) 1 [12] F.D. Gunstone, M.R. Pollard and H.S. Vedanayagam, unpublished observations [13] N.W. Gilman and B.C. Holland, Chem. Phys. Lipids 13 (1974) 239 [14] A.P. Tulloch and M. Mazurek, Lipids 1l (1976) 228